Magnetic control of arc in strip plating

ABSTRACT

A flat coil is positioned adjacent the plating zone with the long sides of the coil parallel with the plating zone. With a pulsating current directed through the coil, the magnetic field produced by the coil controls the movement of an electric arc between the workpiece being plated and the plating strip.

O Umted States Patent 1 1 3,659,075 Pellkofer 1 Apr. 25, 1972 s41 MAGNETIC CONTROL OF ARC IN 2,809,277 10/1957 Breymeier ..219/123 STRIP PLATING 2,809,278 10/1957 Persson ...219/123 3,130,294 4/1964 Regnauld ..219/l23 [72] Inventor: Dieter Pellkofer, Winterthur, Switzerland F l N PA N A [73] Assignee: Sulzer Brothers, Limited, Winterthur, ORE G TE TS OR PPLICATIONS Switzerland 27,941 12/1968 Japan ..219/123 [22] Flled: 1970 Primary E.taminerR. F. Staubly [21] A 1. No.: 6,465 Assistant ExaminerGeorge A. Montanye Attorney-Kenyon & Kenyon Reilly Carr & Chapin [30] Forelgn Appllcatlon Priority Data I 57] ABSTRACT Jan. 29, 1969 Switzerland 1333/69 A flat coil is positioned adjacent the p g Zone with the g I N 19 219 73 9 1 sides of the coil parallel with the plating zone. With a pulsating g u 4 current directed through the coil, the magnetic field produced 58 Field of Search ..219/76 124 122 123 by the "mvemem electric arc the workpiece being plated and the plating strip. [56] References Cited UNITED STATES PATENTS 483,425 9/1892 Coffin ..219/137 12 Claims, 4 Drawing Figures PATENTEDAPR 25 I972 3. 659 O75 Inventor.-

DIETEF? PELLKOF'EF? MAGNETIC CONTROL OF ARC IN STRIP PLATING This invention relates to a plating apparatus and a method of plating.

I-Ieretofore, it has been known to plate various members or workpieces by creating an electric are between the workpiece and a plating material such as a metal strip and by melting the strip in the are so as to deposit the melted material of the strip on the workpiece. It has also been known to move the workpiece relative to the plating material so as to deposit the melted material in a generally linear plating zone. However, it has been found that in these previous techniques, the arc has had a tendency to travel backwards and forwards across the width of the strip in an uncontrolled manner or has stopped still at one end of the melting edge. In either case, the strip melts unevenly and surface defects appear in the plating layer on the workpiece.

Accordingly, it is an object of the invention to control the electric arc of a plating apparatus for plating workpieces.

It is another object of the invention to plate workpieces without surface defects.

It is another object of the invention to plate workpieces in a uniform manner.

Briefly, the invention provides an apparatus and method for plating which utilizes a magnetic field for controlling the electric are used to melt the plating material for depositing onto a workpiece.

This apparatus of the invention is used in combination with a workpiece to be plated, a plating material aligned over the workpiece and a means such as a welding rectifier for creating an electric are between the workpiece and plating material to melt the plating material. The apparatus includes a flat coil which is positioned adjacent the plating zone with the long sides of the turns of the coil generally parallel with the plating zone and a current supply means arranged to supply the coil with pulsating current.

The plating method of the invention comprises the steps of striking an arc between the edge of a metal strip and the workpiece to melt metal from the edge of the strip, feeding the strip towards the workpiece as the strip is melted, moving the workpiece transversely relative to the strip, and controlling the arc by means of a magnetic field established by a flat coil located adjacent the arc and having the straight portions of its turns substantially parallel with the melting edge of the strip, the coil being supplied with a pulsating current.

The term flat coil as used herein is intended to refer to a coil which, in a plane perpendicular to the lines of magnetic forces through the coil, is substantially larger in one direction than in the direction perpendicular to this direction and the turns of the coil may therefore be said to have long sides and short sides.

It has been found that the use of a flat coil in the manner described produces highly satisfactory results with plating strips of considerable width.

These and other objects and advantages of the invention will become more apparent from the following detailed description and appended claims taken in conjunction with the accompanying drawings in which:

FIG. 1 illustrates a simplified diagrammatic vertical section through an apparatus according to the invention;

FIGS. 2 and 3 graphically illustrate two alternative forms of voltage fluctuation for the pulsating current delivered to the coil according to the invention; and

FIG. 4 illustrates a second form of apparatus having a modified flat coil according to the invention.

Referring to FIG. I, a workpiece 1 which is to be plated and which may be a plate for the wall of a ferritic-steel vessel is mounted for movement by a traversing means (not shown) in the direction of an arrow 20 when the apparatus is in operation. A strip 2, for example, of austenitic steel, is provided as the plating material and is mounted above the workpiece l. The strip 2 is moved continuously downwards towards the workpiece 1 by two pairs of feed rolls 21. The strip 2 is connected to the negative pole of a welding rectifier 3, of which the positive pole is connected to the workpiece I. The lower end of the strip 2 is enclosed in a hopper 5 filled with welding flux 6. In advance of the strip 2 with respect to the direction of advance of the workpiece l and in the vicinity of the melting edge, there is a flat coil 10, the straight portions of whose turns are substantially parallel to the melting edge of the strip 2. The coil 10 has a core 11 of ferromagnetic material and is inclined at an angle of approximately 30 to the surface of the workpiece 1 to be plated. The width of the coil is approximately equal to the width of the strip 2. The coil 11 is connected to a generator 12 which functions to supply the coil 11 with a pulsating current having a voltage waveform as indicated in FIG. 2. This current may be periodically increasing and decreasing direct current or conventional alternating current. The frequency of the current is adjustable in the generator 12. Also, preferably, the peak values E and E (FIG. 2) can be adjusted so that the zero-axis crossing of the current can be changed.

The inclination of the core 11 relative to the workpiece surface is such that the magnetic field induced by the current passing through the coil 10 has a plane of maximum magnetic force which passes through the workpiece surface at a point in the plating zone through which the arc 4 passes.

While the apparatus is operating, a direct-current voltage is applied as is known between the workpiece 1 and strip 2, and an are 4 is struck between these two components. The are 4 causes the bottom edge of the strip 2 to melt, and the molten material is deposited in a generally linear plating zone beneath the bottom edge of the strip to form a plating layer 7 on the workpiece 1. Some of the welding flux 6 also melts, forming a layer 8 of slag which is covered by a layer 9 of unmolten flux. As a result of the magnetic field produced by the energized flat coil 10, the are 4 travels back and forth across the width of the strip 2 in a controlled manner and so causes uniform melting. That is, as is known, the magnetic field produces a force proportional to the current in the are 4 since the are 4 acts as a conductor between the strip 2 and workpiece 1. This force which is directed in a direction perpendicular to the are 4 (i.e., conductor) and to the magnetic field serves to propel the arc 4 across the gap between the strip 2 and workpiece 1. However, as the plane of maximum magnetic force is oriented to pass through the base or foot of the are 4 rather than at a point at the top of the are 4 as in the past, the are 4 is moved uniformly along the workpiece 1. By adjusting the displacement of the peak values E and E from the zero axis and by altering the frequency (for which values between 0.1 and 10 II: have proved satisfactory when welding flux is used), optimum conditions can be produced for the fonnation of the plating layer 7. The are is guided backwards and forwards uniformly according to the frequency selected, so that the melting of the strip 2 is correspondingly uniform.

Instead of the voltage waveform shown in FIG. 2, the generator 12 may be arranged to supply the coil 10 with a sawtooth waveform as shown in FIG. 3. A voltage fluctuation of this kind makes the thickness of the plating layer 7 particularly uniform.

Referring to FIG. 4, the flat coil 10 can have a core II which has a portion which projects below the coil and is curved about an axis 22 parallel to the melting edge and situated on the strip side of the core. As shown in broken lines, the core 11' may also have a portion which projects above the coil and is curved about an axis 23. Alternatively, the core may be curved in such a way that the axis of curvature lies to the left of the strip 2 in FIG. 4, at point 24.

The forms of apparatus described may be used for plating without using welding flux, as FIG. 4 shows, or an inert gas or an inert-gas mixture may be fed to the melting edge instead of welding flux, the frequency of the pulsating current supplied to the flat coil possibly having values which are other than those stated above, and which can be obtained empirically.

What is claimed is:

1. In combination with a workpiece to be plated, a plating material strip mounted above said workpiece, and means for creating an electric are between said workpiece and said strip to melt said strip and to deposit a plating layer on said workpiece to one side of said strip in a generally linear plating zone; means between said workpiece and said strip for creating a magnetic field having a plane of maximum magnetic force passing through said workpiece at a point in said plating zone for imposing a force on said electric arc to move said electric arc across said workpiece.

2. The combination as set forth in claim 1 wherein said means includes a flat coil and a core of ferromagnetic material within said flat coil, said core having an end inclined with respect to said workpiece and said strip to direct said plane of maximum magnetic force towards the base of said are.

3. The combination as set forth in claim 2 wherein said means further includes a current supply means for supplying a pulsating current having predetermined peak values to said coil.

4. The combination as set forth in claim 3 wherein said current supply means includes means for adjusting the pulsating current in frequency.

5. The combination as set forth in claim 3 wherein said current supply means includes means for adjusting the peak values of the pulsating current.

6. The combination as set forth in claim 1 wherein said means includes a flat coil and a core of ferromagnetic material within said coil, said core having a curved end portion projecting from said coil and directed towards said workpiece to direct said plane of maximum magnetic force towards the base of said are.

7. The combination as set forth in claim 1 which further includes means for moving said workpiece transversely relative to said strip, and means for moving said strip towards said workpiece.

8. The combination as set forth in claim 1 which further comprises feed means adjacent said plating zone for feeding flux thereto.

9. A method of plating a workpiece which comprises the steps of moving the workpiece transversely relative to a metal strip, striking an are between an edge of the metal strip and the workpiece to melt the strip and deposit a plating layer on the workpiece to one side of the strip during movement of the workpiece, and creating a magnetic field having a plane of maximum magnetic force passing through the arc and the workpiece at a point below the metal strip to uniformly move the arc across the workpiece.

10. A method as set forth in claim 9 wherein a pulsating current is generated in a flat coil about a core inclined to the strip and workpiece to generate said magnetic field and to move said are reciprocally across said workpiece.

11. A method as set forth in claim 10 wherein said pulsating current is varied in frequency between 0.1 and 10 Hz.

12. A method as set forth in claim 10 which further comprises the step of supplying flux to the vicinity of the arc during movement. 

1. In combination with a workpiece to be plated, a plating material strip mounted above said workpiece, and means for creating an electric arc between said workpiece and said strip to melt said strip and to deposit a plating layer on said workpiece to one side of said strip in a generally linear plating zone; means between said workpiece and said strip for creating a magnetic field having a plane of maximum magnetic force passing through said workpiece at a point in said plating zone for imposing a force on said electric arc to move said electric arc across said workpiece.
 2. The combination as set forth in claim 1 wherein said means includes a flat coil and a core of ferromagnetic material within said flat coil, said core having an end inclined with respect to said workpiece and said strip to direct said plane of maximum magnetic force towards the base of said arc.
 3. The combination as set forth in claim 2 wherein said means further includes a current supply means for supplying a pulsating current having predetermined peak values to said coil.
 4. The combination as set forth in claim 3 wherein said current supply means includes means for adjusting the pulsating current in frequency.
 5. The combination as set forth in claim 3 wherein said current supply means includes means for adjusting the peak values of the pulsating current.
 6. The combination as set forth in claim 1 wherein said means includes a flat coil and a core of ferromagnetic material within said coil, said core having a curved end portion projecting from said coil and directed towards said workpiece to direct said plane of maximum magnetic force towards the base of said arc.
 7. The combination as set forth in claim 1 which further includes means for moving said workpiece transversely relative to said strip, and means for moving said strip towards said workpiece.
 8. The combination as set forth in claim 1 which further comprises feed means adjacent said plating zone for feeding flux thereto.
 9. A method of plating a workpiece which comprises the steps of moving the workpiece transversely relative to a metal strip, striking an arc between an edge of the metal strip and the workpiece to melt the strip and deposit a plating layer on the workpiece to one side of the strip during movement of the workpiece, and creating a magnetic field having a plane of maximum magnetic force passing through the arc and the workpiece at a point below the metal strip to uniformly move the arc across the workpiece.
 10. A method as set forth in claim 9 wherein a pulsating current is generated in a flat coil about a core inclined to the strip and workpiece to generate said magnetic field and to move said arc reciprocally across said workpiece.
 11. A method as set forth in claim 10 wherein said pulsatIng current is varied in frequency between 0.1 and 10 Hz.
 12. A method as set forth in claim 10 which further comprises the step of supplying flux to the vicinity of the arc during movement. 